Once again I'm here to give some bad news. Once again most is very well done but some basics have been missed. Once again most of my critique is involving your magazine region. First off, the magazines lack proper modern feed lips sterotypical of any modern magazine that'd allow for loading into the weapon. If possible go to a local gunstore and just take a look at used magazines for the design of the feed lips. It's better than looking online when you can see and feel your refferance piece in your hands.
In regards to the way it's stashing additional ammo. It's fairly reasonable to allow more than one magazine to be attached by from the available views you don't allow any form of magazine release to be seen so despite most details being there that one in particular is completely missing.
Another node in regards to the magazine. Magazines for man portable rifles and handguns are never thicker than 1/16nth of an inch, and in some designs are as thin as 1/32nd of an inch without issues, yet you have a insanely thick design. Given the perportions of the bullets depicted in the exposed magazines is that it's an enlarged pistol type round to rifle specifications similar to the VKS sniper. And .50 Beowulf Ar-15 upper recievers. While bullets of that size can be used for respectable range it doesn't give the feeling that the bullet matchs the purpose given by the fire-arm. Mainly because of it's scope.
The only real other things I suggest is moving the grenade launcher to under the hand guard so the launcher is closer to the muzzle of the weapon for optimal ballastics. This will allow for a bi-pod to be placed reasonably under the rifle in the launcher's current position without causing any faults in practicality.
And finally my last suggestion. A seam on the body of the rifle that marks the separation between the upper and lower halves of the weapons so there's more clear definition of the weapon sections. It's a tad tricky for bullpups but it's still feasible.
Not sure what the rifle is designed for. The size and scope would indicate long distance, high accuracy, but the size of the magazines would suggest medium-range ammunition, possibly high RoF, whereas the grenade launcher would suggest short range. While technically, it could be multi-purpose, it would be very unwieldy and heavy.
From a technical standpoint, very well done, high level of detail
Please state in your description that you want critique on this piece, for it is demanded for submission in the "critique" gallery folder of #3D-Artists as listed here > [link]! I'm sorry for this little inconvenience, but that's the rules of the group. I don't wanna see your piece being deleted from the folder.